In 4-wheel drive automobiles, a wheel bearing apparatus exists where the driver can selectively switch front wheels or rear wheels to driving wheels or driven wheels using a clutch. Such a wheel bearing apparatus 50, with the clutch function, includes, as shown in FIG. 6, a wheel hub 52 coaxially mounted on an axle 51 of a driving train. A double row tapered roller bearing 53, as the rolling bearing, is mounted on the wheel hub 52 at its axially center portion. A gear member 54 is axially juxtaposed by the double row tapered roller bearing 53. In addition, the wheel bearing apparatus 50 is coaxially supported on the axle 51, via a deep groove ball bearing 55. A needle bearing 56 is arranged between the axle 51 and the wheel hub 52. A reference character “G” denotes a slide gear.
The wheel hub 52 includes a cylindrical portion 57 formed coaxially with the axle 51. A flange 58 radially extends from the cylindrical portion 57 near the outer-side end. A caulked portion 59 is formed by bending an inner-side end of the cylindrical portion 57 radially outward. A hub-splined portion 60 includes a plurality of spline recesses (spline grooves) 60a and a plurality of spline projections 60b. The recesses 60a and splines 60b are alternately arranged between each other on the outer circumference of the cylindrical portion 57 near the caulked portion 59. The hub-splined portion 60 is engaged with an inner circumferential splined portion 61. The circumferential splined portion 61 includes spline recesses 61a and spline projections 61b. Both are formed on the inner circumference of the gear member 54. The flange 58 is formed with a plurality of through apertures 58a. Fastening members BO, such as bolts, are inserted through apertures 58a to fasten a wheel (not shown).
The double row tapered roller bearing 53 includes an inner ring 62, an outer member 63, and double row tapered rollers 64, 65 juxtaposed in an axial direction between the inner ring 62 and the outer member 63.
In more detail, the inner ring 62 includes a first inner ring member 66 and a second inner ring member 67. The first inner ring member 66 includes a first raceway surface 66a. The second inner ring member 67 has a second raceway surface 67a. The first inner ring member 66 and the second inner ring member 67 are arranged to abut against each other. An outer-side end face 66b of the first inner ring member 66 abuts against a root portion of the flange 58 of the wheel hub 52. The inner-side end face 67b of the second inner ring member 67 abuts against an end face of the gear member 54. Accordingly, the gear member 54 and the inner ring 62 (first and second inner ring members 66, 67), forming the double row tapered roller bearing 53, are firmly secured so as not to be rotated relative to the wheel hub 52.
On the other hand, the outer ring 63 includes a first raceway surface 63a, a second raceway surface 63b, and a flange portion 63c extending radially outward. The flange portion 63c is adapted to be secured to a steering knuckle (suspension apparatus) of a vehicle. A numeral 68 denotes sealing members.
The gear member 54 has a generally annular configuration. It is axially juxtaposed by the second inner member 67 so that it abuts against the end face 67b of the second inner ring member 67. The outer circumference of the gear member 54 is formed with a plurality of spline recesses (spline grooves) 69a and a plurality of spline projections 69b. Together, they form an outer circumferential splined portion 69. The outer circumferential splined portion 69 is adapted to engage with a splined portion G1 of the gear ring G.
As shown in FIG. 7, the inner circumferential edge, at its inner-side of the spline projection 61b of the inner circumferential splined portion 61 of the gear member 54, is chamfered to form an inner-side chamfered portion 70 with a curved surface. The chamfered portion 70 is designed to be positioned inner-side of the splined portion 60 of the wheel hub 52. In particular, it is designed so that a distance L is smaller than a distance X. The distance L is a distance from the inner-side end face 71 of the gear member 54 to the outer-side end 71a of the chamfered portion 70. The distance X is a distance from the inner-side end face 71 of the gear member 54 to the end point 60c of the spline recess 60a of the hub-splined portion 60 of the wheel hub 52. Thus, it is possible to increase the bending radius of the caulked portion 59 formed on the inner-side end of the cylindrical portion of the wheel hub 52. Accordingly, this effectively suppresses the generation of cracks in the root of the caulked portion 59 (e.g., see Patent Document 1 Japanese Patent No. 4466302.
As described above, it is possible in the prior art technology wheel bearing apparatus to increase the bending radius of the caulked portion 59. Accordingly, this effectively suppress the generation of cracks in the root of the caulked portion 59. When the driving torque is inputted to the gear member 54 from the driving/non-driving switching system, the gear member 54 transmits the driving torque to the wheel hub 52 via the inner circumferential splined portion 61. Although the inner circumferential splined portion 61 of the gear member 54 is hardened by heat treatment, the hub-splined portion 60 of the wheel hub 52 is rare and not hardened. Thus, allowable torque of the hub-splined portion 60 is limited and therefore it is required to reduce the torque applied to the hub-splined portion 60.